Add instructions

Author: vollborn

README.md

@@ -2,7 +2,33 @@
 
 JetBrains Gateway SSH was made to provide a clean SSH server for JetBrains Gateway.
 
-## Setup
+## Getting started
+
+JetBrains Gateway SSH is pushed to Docker Hub. You can use this docker-compose.yml example to quickly start a container:
+
+```
+version: "3.1"
+services:
+  jetbrains-gateway-ssh:
+    image: vollborn/jetbrains-gateway-ssh
+    environment:
+      SSH_USERNAME: "${SSH_USERNAME:-jetbrains}"
+      SSH_PASSWORD: "${SSH_PASSWORD:-jetbrains}"
+    volumes:
+      - "./home:/opt/home"
+    ports:
+      - "${SSH_PORT:-22}:22"
+```
+
+You should change the default password and username by creating an .env file with your own credentials:
+
+```
+SSH_PORT=22
+SSH_USERNAME=jetbrains
+SSH_PASSWORD=myownpassword
+```
+
+## Development
 
 1. Clone the repository
 ```shell